1. Field of the Invention
The invention relates to an air-assisted wiping device. More particularly, the invention relates to an air-assisted wiping device for wiping the inside walls of a continuous-type spray dryer.
2. Description of the Related Art
In the food industry, dryers are used in the manufacture of powders. Liquid products of various viscosities and stickiness are introduced into the dryer through the use of an atomizer. As a result of gravity, the atomized liquid passes through the dryer and the atomized liquid is flashed into powder.
There are primarily two types of dryers used in the industry, a batch dryer and a continuous spray dryer. The batch dryer is often referred to as a box dryer because it is essentially a box-shaped housing having an inlet at the top and an outlet at the bottom. The products are produced in finite batches rather than continuously as in the continuous spray dryers. The air in the batch dryer housing is heated by conventional techniques. The fluid product is input into an atomizer at the inlet of the box and is atomized into a fine mist, which disperses into the heated air inside the housing. The atomized liquid falls through the housing from the top to the bottom due to gravity. As the atomized liquid passes through the heated air in the housing, the heat in the dryer flashes away the moisture in the atomized liquid. As a result, by the time atomized liquid reaches the bottom of the housing, it is in a dried powder form. The dried powder falls out of the bottom of the batch dryer and collects in an area below the batch dryer. The collected powder is then transported to the next stage of manufacturing by, for example, shoveling.
During operation of the batch dryer, the powder collects on the walls of the housing. If the powder remains the walls for an extended period of time, it will become scorched and effect the quality of the powder produced. Although powder collects on the walls of the housing during the production of all types of powders, the collection is especially high and the collected powder especially difficult to remove when heavy sticky powders are being manufactured.
This problem occurs in both batch and continuous dryers, however, the removal of the powder from the walls differs for each type of dryer. In the batch dryer, the dryer walls are manually cleaned after each batch by conventual techniques such as scraping, thus the use of the batch dryer is labor intensive.
The continuous spray dryer is usually of a cylindrical shape, having a funnel or conical-shaped discharge end for channeling the powder into a discharge chute. The liquid is atomized and dried inside the housing in a manner similar to the batch dryer. However, this type of dryer operates continuously to both manufacture discharge powder through the chute at a bottom end of the funnel-shaped discharge end. This continuous-type dryer can be used continuously because an air broom is provided in an attempt to continuously clean the inside of the walls. The conventional air broom used in continuous spray dryers consists of an elongated hollow pipe that has a blunt open end or a series of openings along a side of the pipe that is positioned adjacent to the inside wall of the housing. The air broom is moved over the inside walls of the housing. The streams of air expelled from the openings blow on the inside walls of the continuous spray dryer in an attempt to blow off the powder that has collected on the inside walls of the housing.
Use of the conventional continuous spray dryer, however, is limited to light-weight, non-sticky liquid products because the heavy sticky types of powder tend to collect on the wall and cannot be removed by conventional cleaning techniques used in the continuous spray dryers. The quality of the powder is therefore compromised and inferior since the powder sticks to and cannot be removed from the walls. Heavy sticky powders are therefore conventionally manufactured in the batch dryers, which can be manually cleaned after each batch.
Some examples of such heavy sticky products include butterfat, high carbohydrate and/or high acid powders such as acid cheese whey, acid casein, caseinates and potato waste water.